Abstract
It has been shown that a) the membranes of HeLa and L cell lysosomes are readily permeable to naphthol AS-AM phosphate when used as a substrate for acid phosphatase, b) freezing as well as fixation affect the permeability of the lysosomal membrane to both naphthol AS-AM phosphate and β-glycerophosphate, c) none of these treatments seem to affect greatly the plasma or the mitochondrial membranes and d) the distribution of phospholipids in the cells is also affected by freezing or fixation.